This invention relates to a method and system for supplying fuel to an automotive engine. More particularly, this invention relates to a method and system for supplying fuel to an internal combustion engine from a multiple fuel supply contained in a single fuel tank.
Transportation is unique among the energy-consuming sectors of the economy in that it is totally dependent on one source of fuel: crude oil. Because of the shortage of domestic petroleum, coal and oil shale are being considered as sources of petroleum substitutes. There are a number of possible process routes from shale or coal to liquid fuels suitable for the transportation market that may be economically competitive with gasoline from crude oil. Of these, however, only methanol-from-coal is based on existing technology.
Methanol has been used in motor vehicles either pure or blended with gasoline. Sufficient data exists to support the feasibility of using methanol in automobiles, and in fact limited emissions data suggest that methanol may provide a very effective means of achieving strict emissions goals as well as improved engine efficiency.
A number of problems arise when considering modification of the complex infrastructure associated with United States transportation to include methanol. Commonly listed are phase separation in methanol blends, difficulty with cold starts with straight methanol, limited initial availability of a new fuel, materials compatibility, and vapor lock and driveability associated with blends when used in current autos. Gasoline and methanol blends are subject to phase separation in the presence of small quantities of water, as shown in the equilibrium phase diagram, FIG. 1. With conventional fuel supply systems, such separation causes engine malfunction. Various special precautions have been proposed to prevent such separation. For example, it has been proposed to add a small amount of ethylether, acetone, butanol, or cyclohexanol to prevent to some extent the separation of methanol, but these additives are too costly to be used in gasoline. It has also been proposed to use two separate fuel tanks, one for each fuel.
To facilitate introduction of methanol into the automotive market, particularly when widespread availability may not be guaranteed, cars must also be able to run on either gasoline (including synthetic gasoline) or methanol (or blend of alcohol fuels). Thus, the need exists for a practical approach which solves the problems associated with the introduction of methanol fuel, particularly the difficult problem associated with water-induced phase separation.